Feeding Your Rotifers - Instant Algae® Rotifer Recipes

Instant Algae® products are excellent feeds for producing large quantities of highly nutritious rotifers. Microalgae are the natural food for rotifers and provide the highest growth and fertility rates of any rotifer feed. By using a combination of Instant Algae® products you can create the optimal EPA / DHA / ARAprofile for your target species.

Rotifers do not intrinsically possess high nutritional value - rather they act as "nutrient carriers" for conveying the high-value essential fatty acids (ARA, EPA and DHA) and other nutrients from the microalgae to the target species. Although you can feed rotifers a variety of feeds such as yeast, the rotifers will only be as nutritious as the feed they have ingested—“they are what they eat”. A rotifer that is fed insufficient or low-quality feed will provide little nutritional value to your larvae.

Marine microalgae is widely recognized as the best feed for growing and enriching rotifers. Microalgae are what rotifers naturally feed on in the wild, and provides the complete chemical composition that larval fish need for proper neural development. Microalgae are also the easiest feed to work with. Yeast and emulsion products rapidly foul a rotifer cultures, creating high levels of bacteria and ammonia, and causing the rotifers to stick together. Microalgae such Nannochloropsis have a cell wall that resists bacterial breakdown so there is no fouling, excessive bacterial proliferation, or stickiness.

Note: The following is general information. As with any type of live culture, for optimal results you must adapt your practices according to your own situation

Feeds for optimal growth and fertility

The best feed for growing rotifers is 100% Nannochloropsis. Nannochloropsis is a small alga (2 µm ) that has a very high lipid, protein, and calorie content. This alga will give your rotifers a very high nutritional and EPA profile. We recommend 1.5 ml of Nannochloropsis 3600 for each 1 million rotifers each day.

Feeds for DHA Enrichment

The best algae for DHA enrichment are either Isochrysis or Pavlova which contains 10% DHA as a percentage of lipids. DHA enrichment is done during the last 4-8 hours before feeding the rotifers to your animals. We recommend 3 ml's of Isochrysis or Pavlova for every 1 million rotifers each day.

How much to feed

The following information is based on Reed Mariculture's observations from growing "L" type rotifers at our facility, using a simple continuous culture system.
Rotifers are voracious animals - a single (L) strain rotifer will consume about 115,000 cells of Nannochloropsis each day. Instant Algae®Nannochloropsis 3600 contains 68 billion cells per ml (68 trillion per bag) and will feed about 600 million (L) rotifers or 1 billion (S) or (SS) rotifers each day. In low density cultures (< 1,000 / ml) you will find that the rotifers need about 1/3 more algae than in high density cultures.

Nannochloropsis is the best single alga we have found for growing rotifers. We recommend 1.5 ml of for each 1 million "L" type rotifers each day. If you are using S or SS type rotifers use 1.5 ml for each 2-3 million rotifers.
For DHA enrichment we recommend 3 ml of Isochrysis or Pavlova for every 1 million "L" type rotifers each day. If you have S or SS type rotifers feed 3 ml for each 2-3 million rotifers.

How often to feed

The key to successfully maintaining a rotifer culture is keeping the right amount of algae in the water at all times. If you add too much algae it will not be eaten and will create detritus and proliferation of bacteria. If you add too little algae your animals will be hungry and become "shocked".

Unlike larger animals that can store significant metabolic reserves, rotifers need to feed continuously. Due to their high metabolism, about 2-4 hours after a pulse feeding their guts will be empty and they begin to starve, a physiological shock that disrupts their reproduction. Rotifers need a consistent supply of algae in the water at all times, allowing them to graze continuously. Fortunately, setting up a continuous feeding system is easy and inexpensive.

Setting Up a Continuous Feed System

Once or twice each day fill a jar or bucket with water from your tank and add the measured amount of microalgae formula (see above for amount to use)

Place the feed reservoir above the tank and use a plastic hose to establish a siphon into the tank. Regulate the flow by pinching the hose with a clip until it slowly drips the algae into the tank at a steady rate. If possible, put an air stone in the bucket to maintain aeration

OR purchase a small metering pump ($150-200) and timer to dose the tank frequently

If you are in a warm climate you will need to keep the jar of algae concentrate cool. Putting a cool object in the jar with the algae can maintain proper temperatures. Some hatcheries use gel ice bags and rotate them between the freezer and the jar of algae concentrate every 6-12 hours

Ammonia Control

Ammonia toxicity is one of the greatest challenges with rotifer production. Rotifers have a very high metabolism and produce a lot of waste, of which a major fraction is ammonia that can quickly reach toxic levels. We use (and sell) an ammonia neutralizer called ClorAm-X® with our rotifers, both in our culture tanks and for shipping the animals. We use about 150 grams of ClorAm-X® for each 1 liter bag of Nannochloropsis 3600, or 600 million rotifers.

Microalgae Ice Cubes

Instant Algae®Nannochloropsis 3600 can be frozen into small ice cubes, which has the dual benefit of creating a pre-measured quantity of algae, and extending the shelf life of the product. To make microalgae ice cubes simply pour the algae into plastic ice cube trays and place in the freezer overnight. When frozen, break the cubes out of the trays and store them in a plastic bag in your freezer. By weighing one of the cubes you will know the size of all the cubes, simplifying your future feeding protocol. As needed, take as many cubes as needed from the freezer and disperse them in a container with the same water as used for your rotifer culture (see "continuous feed system" above). If you have extra algae remaining store it in your refrigerator where it will keep for several days.

Improving Culture Performance

The key to optimized and reliable rotifer cultures is stability of the culture conditions. There are several variables that can "shock" your rotifers, decreasing their growth and fertility rates. The most common are a changes in temperature, pH, salinity, or food availability in the rotifer culture. Typically these "shocks" come from feeding large volumes of live algae cultures but can also be caused by other factors.

Microalgae are plants, and require large amounts of plant fertilizers such as nitrate or ammonia , phosphate , and iron. These are good for plants but can be somewhat toxic for animals. Microalgae cultures can have higher pH levels than rotifer cultures due to photosynthesis. For best growth and nutritional value algae are typically grown at 16-24 °C whereas rotifers are grown at 26-30 °C. When the algae culture that is full of fertilizers, has a different pH, and a lower temperature is introduced into your rotifer culture, it "shocks" the culture. This can cause weak animals to die, healthy animals to stop feeding for a time , and interrupt egg production.

Algae concentrates provide several advantages over live algae in rotifer cultures:

During the harvesting process most of the fertilizers are removed from the algae along with the water

When the algae concentrate is added to the rotifer culture the salinity and pH in the tank is virtually unaffected because the volume of the added algae is so small

Temperature remains stable because the slow drip of concentrated algae is so small that it does not affect the tank temperature

For these reasons you will find that almost all commercial high density ( > 1,000/ml) rotifer bioreactors use algae concentrates rather than live algae cultures.

Tips for Starting a Rotifer Culture

Feed rates should be based on the actual density of rotifers in the system and care should be taken not to overfeed

If feeding continuously the drip rate should be monitored to avoid excess algae accumulation

If batch feeding, the culture tank should clear of algae before the next feeding to avoid excess algae accumulation

Any algae that is not consumed within 48 hours will degrade, increasing the level of ammonia and decrease the dissolved oxygen levels

Care should be taken to match the salinity of the rotifer tank to the salinity of the starter culture

Low Density Rotifer Culture (10-300 rotifers per ml)

Reef hobbyists, aquarium stores and small and large hatcheries use low density rotifer cultures to provide feed to larval fish. Instant Algae® products can be used as a complete replacement for live algae.

Sterilized seawater should always be used to fill rotifer culture tanks. The water should be adjusted to the optimal pH and temperature for the starter culture. Cultures should be started with a minimum of 10-20 rotifers per ml. Generally it is easier to monitor the performance of denser cultures, so if possible start with a smaller volume at higher density and increase the volume as the population grows . Cultures can be maintained on 1-2 feedings per day; however continuous feeding or several smaller feedings per day are preferable.

Rotifer counts should be taken daily to determine the health of the culture. Healthy cultures of rotifers contain egg- bearing females and very few or no males (depending on the strain). An increase in the number of male rotifers, identifiable by their smaller size and lack of a gut, is an indicator of a stressed culture. If this happens, the water quality should be tested and appropriate corrective action should be taken.

In small aquariums (<30 gallons), it is best not to exceed 300 rotifers per ml. As the volume of the culture container increases the density of rotifers can also be increased. (see Table 1 for additional system guidelines). Experienced culturists have exceeded 700 rotifers per ml in batch culture systems. Semi-continuous cultures can be maintained by doing a daily 30-50% water change and rotifer harvest. The culture should rebound and have the same densities the next day, allowing for a daily harvest. Over time, the culture will need to be restarted to avoid waste build-up and bacterial blooms that can cause a culture crash. Semi-continuous cultures can be maintained for a week or more before restarting.

Aeration is needed to keep adequate dissolved oxygen levels and to maintain rotifers and algae cells in suspension. Over-aerating can result in excessive evaporation, foam production and rotifer loss. Lighting is not necessary.

High Density Rotifer Culture (700- 5000 rotifers per ml)

High density rotifer culture is necessary when large quantities of rotifers are needed each day. These can be run as batch cultures or continuous culture systems. H igh density systems must maintain a carefully controlled environment for the rotifers. A pH control system, feed dosing system and pure oxygen additions are necessary to maintain high density cultures. Optimal pH in these systems is 7.0-8.0, which reduces the toxic un-ionized fraction (NH3) of the total ammonia. Continuous high density rotifer systems require waste removal by particulate filtration and chemical or biological ammonia control.

High density rotifer cultures vary in size from 5 to over 250 gallons, or 20-1,000 liters. For beginners it is reasonable to expect 500-700 per ml while more experience culturist can often consistently achieve as much as 5000 per ml. In high density rotifer systems the use of an algae concentrate such as Instant Algae® is necessary to reach the desired densities because of the "shock" factors from feeding large amounts of live algae (see Improving Culture Performance), as well as the high cost of producing the necessary amounts of live algae. The ultimate goal is to obtain the maximum rotifer production in the minimum volume, with efficient use of the feed . DHA e nrichment can be accomplished through the traditional method of feeding Isochrysis in the last few hours before feeding them to your animals, or by feeding RotiGrow® growout/enrichment feeds.

Super High Density Rotifer Culture ( 5,000 - 15,000)

Densities over 15,000 per ml have been exceeded in sophisticated recirculating systems. Whether the effort required to achieve such densities is justified by the yield of such systems has not been widely demonstrated. Unfortunately no detailed guidelines for super high density rotifer culture have been published. If you are interested in developing such cultures, contact us and we will be happy to help you in any way we can.

Information on this page was developed from our own experience, published literature, and consultation with Reed Mariculture customers all over the world. Particularly valuable insights were gained from:

Reed Mariculture is the world's largest producer of marine microalgae concentrates. We supply algal feeds and zooplankton to universities, marine ornamental growers, and over 500 fish, shrimp, and shellfish hatcheries in 80+ countries around the world.

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